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The Subaru Seminar is usually held in Room 104 of the Hilo Base Facility, adjacent to the main lobby. Everyone is welcome to attend. If you are interested in giving a seminar, please contact Subaru seminar organizers (Tae-Soo Pyo, Sherry Yeh, Nagayoshi Ohashi) by email : (please change"_at" to @).

April 15, Wednesday, 11:00 am in 104

" NIR spectroscopy of star-forming galaxies at z~1.4 with Subaru/FMOS "

Kiyoto Yabe


Revealing galaxy properties at z~1-2, where galaxies are in the most active phase, is important to understand the formation and evolution of galaxies. The chemical properties of galaxies such as gas metallicity are also important parameters to examine the galaxy growth, because metallicity traces the past star-formation activity including gas inflow and outflow. However, a large NIR spectroscopic observation is required to measure the gas metallicity of galaxies at z~1-2 by using the rest-frame optical emission lines. Recently, we conduct large NIR spectroscopic surveys with a wide-field NIR spectrograph on the Subaru Telescope, Fiber Multi Object Spectrograph (FMOS). In the FMOS/GTO survey, we obtained significant Ha detections from ~340 star-forming galaxies at z~1.4. In the FMOS cosmological redshift survey (FastSound), which is shallower survey than the FMOS/GTO, we detect Ha emission lines from ~4000 galaxies at z~1.4. We measure the gas metallicity from the [NII]6584/Ha emission line ratio of composite spectra in various stellar mass and star-formation rate bins. The resulting mass-metallicity relation at z~1.4 is between those obtained in previous studies at z~0.8 and 2.2. No clear dependence of the mass-metallicity relation on star-formation rate is found, which is not in agreement with the extrapolation of the local fundamental metallicity relation. We detect the significant [SII]6716,6731 emission lines from the composite spectra. We estimate nitrogen-to-oxygen abundance ratio (N/O) from the N2S2 index, and found that the N/O in galaxies at z~1.4 is significantly higher than the local value at a fixed metallicity. Our sample at z~1.4 with the metallicity recalculated taking into consideration the N/O enhancement is in good agreement with the extrapolation of the local fundamental metallicity relation. This result is an excellent test case for near-future surveys with a next-generation very wide-field multi object spectrograph on the Subaru Telescope, Prime Focus Spectrograph (PFS).

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